1. Field of the Invention
This invention relates to an improved piston for an internal combustion engine.
2. Description of Related Art
The prior German DT 26 07 561 A1 corresponding to U.S. Pat. No. 4,170,966 issued Oct. 16, 1979 to Schmidt entitled "Mixture-Compressing Internal Combustion Engine, Especially Four-Cycle Engine" discloses an internal combustion engine of the generic type with recesses formed in the piston crown of the piston to improve the efficiency of combustion and thus reduce hydrocarbon emissions.
Further references which show internal combustion engines with recesses and depressions formed in the piston crown of the piston are German DE 196 24 227 A1, and DE 29 34 615 A1 and U.S. Pat. No. 3,797,466.
In general, piston configurations with recesses or depressions in the piston crown are used to bring about flow effects including swirling flows of various kinds in the combustion chamber it being the intention to improve the mixing of air and fuel and thus to improve homogenization of the fuel/air mixture, thus increasing combustion efficency.
There is a fundamental distinction between two different types of flow in a combustion chamber: swirling flow which is a vortical motion of the fuel/air mixture about the longitudinal axis of the cylinder of the internal combustion engine; and tumbling flow, on the other hand, which is a vortical motion about an axis parallel to a transverse axis of the cylinder. The aim of the recesses mentioned above is to reinforce the degree of turbulence within the combustion chamber defined by the cylinder or to otherwise deflect such flows.
A disadvantage with the known embodiments of recesses in the piston crown of the pistons of internal combustion engines is the still relatively poor mixing and the consequent stratification of the fuel/air mixture in the combustion chamber and the associated increase in the tendency to knock, despite the efforts made to bring about flow effects.